Pirenzepine is a 'selective' antimuscarinic agent which, unlike classic anticholinergic agents, inhibits gastric acid secretion at lower doses than are required to affect gastrointestinal motility, salivary, central nervous system, cardiovascular, ocular and urinary functions. On a weight basis, pirenzepine has one-tenth to one-eighth the potency of atropine in inhibiting stimulated gastric acid secretion in humans. Extensive controlled trials utilising endoscopy in outpatients with duodenal ulcers indicate that patient response to pirenzepine is dose related. Doses of 100 to 150 mg/day are superior to placebo in promoting duodenal ulcer healing and in diminishing day and night pain and supplementary antacid consumption. At such doses, the efficacy of pirenzepine appears to be superior to that of gefarnate 300 mg/day and generally not significantly different from that of cimetidine 1 g/day in treating duodenal ulcers. A beneficial effect of pirenzepine in the prevention of duodenal ulcer recurrence was apparent in preliminary studies in small numbers of patients, but its efficacy in this regard needs further confirmation and the optimum dosage determined. Less extensive data on the treatment of benign gastric ulcers suggest that pirenzepine 100 to 150 mg/day is superior to placebo and gefarnate 300 mg/day and does not differ significantly from cimetidine 1 g/day promoting gastric ulcer healing. Pirenzepine is well tolerated by most patients, with a low incidence of typical antimuscarinic effects on the gastrointestinal tract, genitourinary system or heart being reported in clinical studies. However, dry mouth and blurred vision are the more common side effects with clinically effective doses. Thus, pirenzepine appears to have relatively selective antimuscarinic activity, although controlled studies comparing pirenzepine and conventional antimuscarinics in patients with peptic ulcer disease have not been reported.